Document WO 2007/044472 A2 describes an efficient or higher luminance light emitting diode assembly which may be formed from a high power light emitting diode chip having a first surface and a second surface, the first surface being mounted to a substrate, wherein the second surface is in intimate thermal contact with a light transmissive heat sink having a thermal conductivity larger than 30 Watts per meter-Kelvin. The LED chip is otherwise in electrical contact with at least a first electrical connection and a second electrical connection for powering the LED chip. Providing light transmissive heat sink doubles the heat conduction from the LED dies thereby avoids excess heating of the phosphor increasing life and/or efficiency and/or luminance and/or a balance of the three.
In remote laser lighting concept, typically phosphor is pumped from one of the surfaces and the generated light by the phosphor needs to be extracted from the opposite surface. In a transparent phosphor total internal reflection, TIR for short, takes place. However, it is known that light emission by the phosphor occurs in all directions. Therefore, it is difficult to avoid light being emitted by the phosphor (phosphor light) propagating in the direction of the pump source, such as a light emitting diode, LED for short, or a laser. In case of a LED phosphor light propagating in the direction of the LED is partially absorbed reducing the efficiency of the system. To sum up, it is difficult to pump a luminescent material from a surface and extract light from another surface with a high efficiency.